1. Technical Field
This invention relates to wireless applications using Time Division Duplex (TDD) technology in Wireless Local Area Network (WLAN), Wireless Local Loop (WLL), Wireless Internet Access (WIA), wireless modem connection with point-to-point and point-to-multipoint applications.
2. Description of the Related Art
Typically in wireless applications, adding on an antenna amplifier and DC injector is a purchaser option. However, when the operating range of wireless applications is long as, for example, between buildings on a campus, the inclusion of an add-on antenna amplifier/DC injector set may become necessary in order to preserve transmission quality. As is well known by persons in the art, every system presents its own set of considerations. For example, different site environments magnify the significant technical, architectural, and environmental differences between different hardware. In many such instances, the use of conventional amplifiers is limited and a single amplifier design cannot and does not have a sufficient useful range to meet many typical applications.
Attenuation between a DC injector and bi-directional amplifier can range from a few dB to more than 20 dB, losses which may be compounded further from substantial cable interconnection lengths running to hundreds of feet. Furthermore, output power from different radio modems vary which requires component matching in order to avoid undesirable additional losses. In view of such considerations, conventional amplifiers require the system installer to carefully evaluate and measure the input RF power at the antenna amplifier and specify the gain of the amplifier. Thus, in order to achieve and maintain acceptable system performance, conventional applications often require the use of different amplifiers with different systems to meet the specific ambient operating criteria. Failure to exercise careful installation and engage in proper maintenance can cause serious operational degradation.
Accordingly, it is an object of the present invention to overcome the problems associated with the prior art.
It is another object of this invention to provide an amplifier maximizing operational capabilities so as to be usable in a broad range of situations and adapted for use over a wide input power range.
A further object of this invention to provide an amplifier that is capable of flexible operational parameters so as to be usable with a broad range of hardware and in a broad range of operational environments.
Still another object of this invention is to provide a standardized amplifier structure which is economical to install and to maintain.
Yet another object of this invention is to provide an amplifier possessing self-adjusting transmit gain.
A further object of this invention is to provide an amplifier embodying an equation providing for self adjustment of amplifier transmission gain.
A further object of this invention is to maintain constant power levels and minimize signal distortion.
These and other objects are satisfied by a combination of an RF antenna, a bi-directional RF amplifier module, a DC injector, a cable, a power supply, and wireless equipment, said RF amplifier module including an RF input power sensor, an RF power level detector for determining if the RF power level is below a select threshold, a transmit gain control circuit, and at least a first and a second switches, said DC injector being connected to said RF amplifier module by said cable and said wireless equipment which may include a radio modem, said cable capable of carrying a bi-directional RF signal and DC power between the amplifier module and the antenna, where the amplifier switches from a transmit mode to a receive mode when the RF power is below said select threshold to maintain substantially constant output power.
Still other objects are satisfied by the method for maintaining substantially constant output from an RF amplifier independent of input power levels where the amplifier operates to produce
Pout=Cxc2x7Kxc2x710VRxc2x710xe2x88x92Bxc2x7Log(Pin)xc2x7Pin=Cxc2x7Kxc2x710VR+B
where B and C are constants, K is the constant amplifier gain, VR is a fixed reference voltage, Pin is the RF input power level, and Pout is the output power.
The present invention, in short, provides for both power level detection and automatic gain control. The invention contemplates automatically (intelligently) adapting the gain to the input power level, cable, and connector loss due to the particular lengths and configuration of a set up. The invention is particularly useful in TDD wireless applications as the circuitry permits the output power level to be intelligently monitored and maintained whereby desired performance can be achieved regardless of the details of the particular TDD hardware configuration and/or installation environment.
The invention is particularly a cost effective solution for xe2x80x9clast-milexe2x80x9d applications, e.g. connectivity between office buildings, for remote monitoring and in rural areas. Presently, the invention is designed for use with direct sequence or frequency hopping spread spectrum radio modems (or wireless equipment such as LAN cards) to boost transmit power amplification and receive signal gain. By including a dynamic power sensor in an amplifier constructed according to the invention, the RF power output level is adjusted by detecting the input signal power. This automatic gain adjustment minimizes distortion and maximizes output power regardless of variations in input levels.
By exploiting the automatic gain control technique of the invention, an antenna amplifier can detect the input power level, automatically adjust its gain, maintain the output power to a specified level, minimize the signal distortion, and maximize transmission distance. Moreover, standardization, simplicity, and low cost, give this invention an advantage over conventional, xe2x80x9cnon-intelligentxe2x80x9d amplifier structures and methods, particularly as applied to TDD wireless applications.
As used herein xe2x80x9cconnectedxe2x80x9d includes physical, whether direct or indirect, hardwired or wireless, or any operationally functional connection.
As used herein xe2x80x9csubstantiallyxe2x80x9d is a relative modifier intended to indicate permissible variation from the characteristic so modified. It is not intended to be limited to the absolute value or characteristic which it modifies but rather approaching or approximating such a physical or functional characteristic.
Given the following detailed description, it should become apparent to the person having ordinary skill in the art that the invention herein provides an antenna mountable, bi-directional amplifier designed to match advanced spread spectrum direct sequence or frequency hopping systems, and to permit extension of the operating range in wireless environment, at for example, frequencies of 900 MHz, 2.4 GHz, and 5.8 GHz (corresponding to current advanced spread spectrum system operational frequencies). In simplest terms the inventive amplifier herein embodies an intelligent algorithm, preferably, combined with Automatic Gain Controlled (AGC) circuits to maintain the output power and prevent transmit signal saturation. The gain automatically adjusts to minimize the signal distortion by sensing input power with an RF so that the desired signal quality can be assured. Moreover, because the invention utilizes TDD mode, it permits a radio device sharing in different time intervals of an antenna with which the amplifier is associated.